Protective relaying system



PROTECTIVE RELAYING SYSTEM Filed ,Oct. 20, 1943 See WITN ESSES:

. INVENTOR fdzz/z'n L. Hrdex ATTORNEY Patented Nov. 16, 1948 PROTECTIVE RELAYING SYSTEM Edwin L. Harder, Forest Hills, Pa., asslgnor to Westinghouse Electric Corporation, East Pitts- --burgh, Pa... a corporation oi Pennsylvania Application October 20, 1943, Serial No. 506,969

14 Claims.

My invention relates to an improved protective relaying system, such as is utilized for tripping circuit-breakers, or otherwise controlling the operation of circuit-interrupting means in a transmission line or other extended electrical circuit, and for other purposes.

An object of my invention is to provide an improved high-speed relaying system in which carrier-current is superimposed on the line in order to obtain a quick response to a fault-condition at any point within the protected line-section. More specifically, my invention provides an all electronic" or tube-type carrier-current relaying system, and particularly a carrier relaying system of the directional-comparison type. as distinguished from the current-comparison type. In the current-comparison carrier system, modulated carrier is utilized to directly compare the BO-cycle line-currents at the two ends of the protected line-section, whereas, in the directionalcomparison system, carrier-current is utilized merely to block the erroneous tripping-operation due to oversensitive fault-detectors at the relaying point, utilizing current-direction, or other line-condition, at the other end of the protected section to maintain carrier-current transmission ii the conditions at that end are such as to indicate that the fault is at some point beyond that end of the protected line-section.

The indications of the trend of the art point to the ultimate adoption oi "all electronic," or at least no moving part," carrier relaying for the protection of transmission lines. This seems to be indicated, not only because of the increased speed of tube-type relays as compared with mechanical relays having moving contact-parts, but also because of the ever-present possibility of chattering, or bouncing, of mechanically moving contact-points in very high-speed relays. While various bounce-suppressing means have been devised, and are being used with. considerable success, at th presently common speeds of highspeed relaying, nevertheless, a carrier-current system which depends, for its accuracy, upon a An important object or my present invention is to provide a "no moving part" carrier-starting mechanism for line-iault-responsive carrier-current systems in general, and particularly for carrier-current systems of the directional-comparison type.

A iurther object oi my invention is to provide means for utilizing a control-circuit relaying voltage or other relaying voltage, and particularly a rectified voltage, produced directly from the faultcurrents, or from some other function of electrical conditions or the protected line or circuit, to directly bias the grid oi the oscillator-tube to a transmitting condition, or to otherwise initiate carrier-current transmission through electronic or tube-type control.

A further object oi my invention has to do with the utilization of means for providing a unidirectional control-circuit or relaying voltage which has a magnitude corresponding to the magnitude of the lowest impedance which is measurable on the several phases of a polyphase line, as by obtaining the difference between a current-responsive relaying voltage and a voltage-responsive relaying voltage. responsive respectively to the line-currents and the line-voltages ot the several phases, compared, in pairs, according to phases. In this manner, I obtain a single relaying voltage, which is responsive to the magnitude of the impedance oi the faulted phase, and I can use this voltage for directly starting carrier-current transmission, by grid-bias control, or, in general, for energizing any kind oi fault-responsive apparatus from said relaying circuit, whether such apparatus be oi the tube-type or mechanical relays.

With the foregoing and other objects in view, my invention consists in the parts, element, combinations, sub-combinations. system and methods hereinafter described and claimed, and illustrated in the accompanying drawing which illustrates my invention as applied as a modification of a common type of modern carrier-current relaying system of the grid-voltage-control type, which is shown in a Lenehan Patent 2,144,499, January 17, 1939, assigned to the Westinghouse Electric 8: Manufacturing Company. I wish it to be understood, however, that my invention is of general application, in many different forms, and in other types of carrier-current systems and control, and I wish it to be understood that the particular system, which I have chosen for illustration, is only an illustrative example of a preferred form 01' embodiment of my invention.

In the drawing,

Figure 1 is an across the line diagrammatic view of the direct-current ,connections and the carrier-starting control of a carrier-current relaying system embodying my invention in an illustrative form of embodiment,

Fig. 2 is a diagrammatic view of the alternating-current connections of the apparatus shown in Fig. 1, and

Figs. 3 and 4 are views, similar to Figs. 1 and 2, of a diilerent form of embodiment, illustrating some aspects of my invention.

In the drawing, I have illustrated only one end of a three-phase line-section 6, which is to be protected, the several phases being distinguished by the letters A, B and C. Only one end of the line is illustrated, as the other end is, or may be, a substantial duplicate of the illustrated end. The protected line-section 5 is illustrated as being connected, at each end, to a three-phase bus 8, through an oil circuit-breaker l, or other circuit-interrupting means which is to be tripped or controlled so as to disconnect both ends of the protected line-section from the rest of the transmission-system, in the event of an internal fault within the protected section. The circuitbreaker 1 is provided with a trip-coil TC, and an auxiliary breaker-switch 1a, which is open when the breaker is open.

My invention is illustrated as being embodied in a carrier-current relaying system, utilizing carrier-current equipment which is diagrammatically represented by a transmitter T and a receiver R which are connected to a coupling transformer 8 which is coupled to the phase-C line-conductor through a coupling capacitor 9, the carrier-current being confined to the protected line-section by means of a wave-trap H.

While I am illustrating my carrier-current equipment in connection with its use for relaying purposes, it will be understood that the same equipment, when it is not in use for relaying, which means, for most of the time, can be used for telemetering or other uses," as set forth in my Patent 2,217,480, granted October 8, 1940.

The carrier-current transmitter T is illustrated as an electronic, or tube-type, oscillator-generator, including a master-oscillator tube l2. The master-oscillator I2 is illustrated, in a simple form, as a three-element tube having a cathode l3, a grid l4, and a plate or anode IS. The grid M, or other control-circuit means, is of such nature that the tube-operation is strongly maintained when the grid-voltage is sufiiciently positive with respect to the cathode, (assuming that a suitable plate-voltage is applied to the tube), and such that tube-operation is substantially blocked when the grid-voltage is made sumciently negative with respect to the cathode. In the particular illustrated embodiment of my invention, the oscillator-tube is of a type which will freely oscillate when the grid-voltage is brought to approximately the same potential as the cathode i3, or when the grid 14 is only slightly negative with respect to the cathode l3, by-an amount depending upon the particular characteristics of the tube, and also depending uponthe voltage of its plate-current source, which is indicated by the terminals 3+ and 3-.

Referring more particularly to the controlsystem shown in Fig. 1, the oscillator-grid i4 is normally given a strong negative bias, with respect to the cathode l3, so that no carrier-current is being transmitted, by connecting said grid to the negative terminal of the station-battery, through a series of serially connected resistors Rl to R5. The cathode I3 of the oscillator tube is usually held at a potential which is close to the positive terminal of the station-battery, through a potentiometerconnection consisting of the resistors R8 and B1.

In accordance with my invention, as shown in Fig. l, I directly control the voltage of the oscillator-grid It, by relaying voltages or controlcircuit voltages which are responsive to the linecurrents, or responsive to the difference between the magnitudes of a line-current and a line-voltage, or, in general, responsive to any predetermined function of electrical conditions of the protected line 5. By line-current and line-voltage, I do not mean any particular phase of star or delta current or voltage, but any function, or component of phase-sequence quantity, of any single-phase or polyphase current or voltage which is derived from the line.

In Fig. 1, the line-current is derived by means of a bank or star-connected line-current transformers i8, which supply energy to four compensators CA, CB, CC and CO, in different phases of the line-current. In this connection, I am utilizing the term phase in a very general sense, so as to include ground or residual-currents, aswell as either star or delta phase-currents. In the particular illustration shown in Fig. 1, star phase-currents are utilized to energize the respective compensators CA, CB and CC, to respond to phase-faults, while the residual current is supplied to the fourth compensator CO, so as to respond to groundfaults. These compensators may be any kind of impedance-device which will produce a voltagedrop responsive to the current traversing said impedance; in particular, I utilize, as compensators, iron-core transformers or inductance devices, having an air-gap so that they will have a considerable self-inductance which acts as either a fixed or an adiustable impedance which is traversed by the current.

As shown in Fig. 1, a relaying voltage is also derived from the protected line, through potential-transformers l1, and .various delta phases of the derived relaying voltages are utilized to energize the respective voltage-responsive compensators or other auxiliary transformers CA',

CB and CC.

To control the grid-potential of the oscillatortube [2 of Fig. the various current-responsive and voltage-responsive derived voltages, as produced in the various compensators CA, CB, CC, CO, CA, CB and CC, are preferably individually rectified, so as to produce unidirectional derived voltages. I have illustrated a conventional rectifying circuit, for each of these relaying voltages, involving rectifiers or other asymmetrically conducting devices l-B. Preferably, also, I utilize capacitors or other voltage-smoothing means l9, for removing some or all of the ripples or pulsations from the various rectified voltages. It will be understood, of course, that any suitable, or more elaborate, means may be utilized for these purposes. Furthermore, any suitable adjusting-means, or pre-setting means, may be utilized, as symbolized by the variable-tum secondary windings 2| of the residual-current compensator CO, and by the variable-turn primary windings 22 of the several voltage-transformer devices CA, CB and CC.

In Fig. 1, the residual-current-responsive rectified relaying voltage, which appears across the terminals 23 and 24 of the residual-current compensator CO and its rectifier and capacitor assembly l8-l 8, is applied between the negative batteryterminal-() and the junction-point between ,the resistors R3 and R4 in the grid-control circuit 01' the oscillator-tube l2, the polarity of this connection being such that the point 25 is given a positive potential, with respect to the negative battery-terminal in response to the magnitude of the'rsidual line-current, or, more exactly, in response to the smoothed-out, double-waverectified, product of the residual current times the self-inductance or other impedance of the compensator 00.. In this manner, when a residual current of a predetermined magnitude is obtained, a sufilcient positive voltage is impressed 1 upon the point 26 of the grid-control circuit to bring the oscillator-grid it substantially or approximately to the potential of the positive battery-bus or sufilciently positive to cause the master-oscillator i2 to begin oscillating, thus starting carrier-current transmission.

In the case of the phase-current response, for responding to phase-faults rather than groundiaults, I may utilize only the current-responsive relaying voltages, but I have illustrated, in Fig. 1, a more elaborate control-system in which the phase-fault detection is obtained in response to line-impedance, or its reciprocal, admittance, rather than by overcurrents. This response is obtained by utilizing the rectified voltage-responsive derived voltage of each phase to buck the rectified current-responsive derived voltage of a corresponding or paired-off phase, in the manner shown for a single phase, in the Goldsborough Patent No. 2,027,226, January 7, 1936, assigned to the Westinghouse Electri 8; Manufacturing Company'. As explained in said Goldsborough patent, while it is generally preferable to rectify the current-responsiv r laying voltage. so as to avoid the disturbing effect of wave-form distortion, it is not altogether essential to rectify these current-responsive voltages, as the alternating derived volta es can be directly utilized.

In accordance with my present invention, how: ever, I have introduced an additional feature, which was not shown in the Goldsborough patent. in connection with electronic impedance-response, as obtained by the dlfierence between current-responsive and voltage-responsive rectified or unidirectional voltages. Thus, I have provided a single phase-fault relaying-circuit 26-21 which receives energy from three parallel-connected sources of relaying voltages, each of these three sources being the difference between the rectified and smoothed-out voltages produced by the respective current-responsive and voltage-respon sive compensators, such as CA and CA, in one pair; CB and GB in another pair; and CC and CC in the third pair.

It is essential that the parallel connections, for these three parallel-connected voltage-sources for the relaying-bus 26-41, shall include rectiflers, whereby whichever source has the highest resultant or diiIerenti-al voltage will feed its voltage substantially entirely to the relaying bus 28-21, and will not dissipate or feed back its energy into the circuits of the sources having smaller resultant voltages. In the illustrated example, as will be clearly seen from Fig. 1, the various rec-tiflers l8 of the phase-current and phase-voltage-responsive output-circuits will perform this function, whereby the largest phase of the resultant differential voltages of the pairs of current-responsive and voltage-responsive voltages will determine the magnitude of the unidirectional voltage which aesarcs appears across the terminals of the relaying bus In order to obtain a, phase-iault-responsive control of the grid-voltage oi the oscillator-tube i2, the largest-phase resultant-voltage which appears across the relaying bus 26-27 is applied across the resistance RI of the grid-control circuit. In this manner, the relaying bus 26-27 is connected between the negative battery-terminal and an intermediate point 28 in the grid-control circuit, said intermediate point 28 being between the resisters RI and R2. The polarity of this connection is such that the point 28 is raised to a positive potential, with respect to the negative batteryterminal in response to the largest difference existing between any phase of the line-current and the properly weighted magnitude oi a corresponding phase or the line-voltage- When this point 28 is raised to a potential which is substantially the same as that of the station-battery and or which is sufficiently positive to start the operation of the master-oscillator l2, carrier-current transmission will be initiated, and it will be maintained as long as this voltage-condition prevails.

In order to prevent the application of unnecessarily large positive potentials to the oscillator-grid it, as a result of exceptionally severe faults, the grid-terminal it may be connected to the positive battery-terminal through a rectifier til which is connected in such polarity as to drain off excessive positive potentials from the grid, while substantially blocking current-flow in the reverse direction.

The rest of the system which is shown in Figs. 1 and 2 is substantially the same as the known control-system which is shown in the above-mentioned, Lenehan Patent 2,144,499. The coils and contacts of each relay are given the same letter-designation or legend, except in the case of the receiver-relay RR, which, as subsequently described, has two coils, an operating or tripping coil RRT, and a restraining or holding coil RRH, these two coils being distinguished by the suilixed letters '1 and H, respectively.

\ ically indicate how the various parts of each relay or element are connected together. The relays and switches are invariably shown in their open or deenergized positions. As shown in Fig. 2, four relaying panels 3|, 32, 33 and 3d, are shown, to provide three panels of phase-fault relaying, and one panel of ground-fault relaying. I have also shown a bank of delta-connected auxiliary current-transformers 35 for supplying delta line-currents to the current-coils 87 of directional and impedance relays, DA and ZA for phase-A, DB and Z8 for phase-B, DC and ZC for phase-C. The directional relays DA, DE and DC have voltage-coils 38, which are energized from appropriate voltages derived from the potential-transformers ll, while the impedancerelays ZA, Z3 and 20 have voltage-coils 39 which are also appropriately energized from the potential-transformers ll. These directional and impedance relay-elements also have appropriately lettered make-contacts which are utilized in the system of direct-current relayconnections, as shown in Fig. 1, the alternatingcurrent connections being shown in Fig. 2.

In the ground-relay panel 34 of Fig. 2, I have shown ground-directional and ground-current relays D0 and 10, having their current-coils 4| energized in the residual circuit of the line-current transformers l8. The ground-directional is direct and instantaneous. that it is accomplished without thelntermediary amazes 7 relay DO also has a polarizing winding 52, which is energized from any suitable source, such as the auxiliary open-delta potential-transformers 48, or by any other suitable means. as well understood in the art. The ground-directional ,and over-current relays DO and I have appropriately lettered relay-contacts which are shown in the direct-current connections of Fig. 1.

In accordance with these direct-current connections, as shown in Fig. 1, each of the linephases A, B and C is provided with a separate relaying-circuit for energizing an auxiliary bus it whenever there is a simultaneous response of the directional element and the impedance element in any one of the three phases, and the energization of this auxiliary bus it is utilized to perform two functions: it directly energizes the operating coil 45 of an auxiliary relay or contactor-switch CSP, and it energizes the tripcoil TC through a make-contact d6 of a receiverrelay RR. The ground-current relaying-response on Fig. 1 utilizes the make-contacts of the ground directional and overcurrent relays DO and 10 to utilize an auxiliary bus 41 which is also utilized to perform two functions, namely, energizing the operating coil d8 of an auxiliary relay or contactor-switch CSG, and energizing the trip-coil TC through a second contact, 89, of the receiver-relay RR.

The receiver-relay RE is of a known type having two windings. One of these receiver coils or windings is a tripping or operating winding RRT, which is shown in Fig. 1 as being energized by the closure of either a make-contact of the CSP relay, or a make-contact 52 of the CSG relay. The'other receiver-relay coil is a holding or restraining winding HRH, which is shown, in Fig. 1, as being directly energized from the tubetype receiver-element R, which is tuned to the carrier-current frequency.

In operation, in accordance with my present invention; carrier-current transmission is started by changing the potential of the grid-terminal 29, from the negative potential of the negative station-battery terminal to a suitable positive potential, which is usually close to the potential ofthe positive bus as previously explained. This may be accomplished, either by the phase-fault-responslve equipment, which controls the potential of the intermediate point 28, or the ground-fault-responsive equipment, which controls the potential of the intermediate point 25. This carrier-currentstarting-control By direct, I mean of any mechanically moving parts, by the direct application of voltages which are directly derived from, and responsive to, a predetermined function of electrical conditions of the protected circuit of the protected line 5, as previousl explained.

The use of wave-smoothing means, such as the various capacitors It, in combination with full-wave rectifiers i8, makes it possible to derive substantially non-pulsatory rectified voltages irom the various functions of the electrical conditions of the protected line, so that the carrier-current transmission does not pulsate, or come on and oil, with various portions of the alternating-current wave of the line-current. or

other electrical condition of the line. The use of a direct application of a line-function-derived voltage assures that the carrier-current transmitting-condition shall be maintained as long as the fault-condition lasts, in the protected linepoint 55 between theresistors R2 and R3, and

to an intermediate point 56 between the resistors R4 and R5 of the grid-control circuit, in the manner which is described and claimed in the Lenehan patent. The connection of the ground-fault control-point 8B closest to the grid-terminal 29 gives the ground-fault relay CSG preference, ovr

the phase-fault relay CSP, in the control of the carrier-current transmission, as set forth in the Lenehan patent. It will be noted these currentstopping relays CSP and CS6 are directionally controlled, through their direct-current controlcircuits which include the respective directional elements DA, DB, DC and D0, which are responsive to the directions of the various phases of the line-currents,

In the relaying system which is shown in Fig. 1, it is known to be desirable that the carrier-starting fault-response shall be more sensitive than the carrier-stopping fault-response, and this same feature is carried out, in my present design, by.

proper choice of the magnitudes of the rectified relaying voltages, which are applied to the intermediate points 25 and 2B of the grid-control circuit, in comparison with the negative biasing voltage oi. the station-battery lin Fig. 3, I have shown a control-system which is somewhat dlfierent from that which is shown in Fig. l. I have simplified the carrier starting control by utilizing only overcurrent responses, for starting carrier, without utilizing the voltageresponsive restraints which produce the impedance-type of response. In Fig. 3, also, the rectifled output-voltage of all four of the current-responsive compensator-s CA, CB, 06 and C0 are connected in parallel, across a single relayingcircuit Gil-6i, so as to obtain a largest-phase" response, as described and claimed in my Patent No. 2,242,950, granted May 20, 1941. The groundcurrent response may be properly weighted, with respect to the phase-fault responses, by properly adjusting the ground-fault-compensator CO, as shown at 23.

In Fig. 3, by grouping together the groundfault and phase-fault carrier-starting responses,

iary tube 53, for amplifying, or responding to, thees rectified voltages appearing across the relaying bus Gt-ti. The auxiliary amplifier-tube 63 is shown, in a simple form, as a three-element tube having a cathode 5%, a grid 55, and an anode 86'. This tube is of a type such that tube-operation is strongly maintained when the grid-voltage becomes suficiently positive with respect to the cathode 5Q, (assuming an adequate plate-voltage), and preferably the tube-type is such that the tube-operation becomes substantially blocked ag n, when the grid-voltage becomes tube 83 is intended to be representative of any controllable tube-means which will provide a good current-flow connection between the point 28 and the positive bus when the gridvoltage becomes slightly larger than a predetermined value, but which will stop the currentconducting operation after the subsidence oi the fault-condition which caused the initiation of the tube-operation.

The amplifier-tube 83 of Fig. 3 may also advantageously be a saturating type tube, that is, a tube in which a very small diflerence in the grid-voltage, at around the critical point which maks the demarcation between operation and non-operation of the tube, causes the platecurrent to suddenly change, from a substantially zero value, to a very large, or saturated," value. In this manner, I obtain a valve-like response to the voltage of the control-circuit til-8i, and I relieve the oscillator-tube it of the requirement that it should have a saturating characteristic in'the sense of being able to oscillate freely and strongly when its grid-potential is close to the border-line between operating and non-operating conditions.

The plate-voltage which is applied to the amplifier-tube 63 should be at least as high as the negative grid-bias which is applied by the station-battery and or sumciently high to give the oscillator-grid it a positive-enough potential to start carrier. If the amplifying tube 63 is not of the saturating variety, its platevoltage should be higher than the negative bias which is imposed by the station-battery and and the output-voltage of theamplifier tube should be applied across the. resistor RI of the grid-control circuit, in the same manner as in Fig. l.

l current phase-fault detectors IA, IB and IC for the impedance-type phase-fault-detectors ZA, Z8, and Z0 of Fig. 2.

I claim as my invention:

1. Fault-responsive relaying-apparatus for a polyphase circuit which is to be protected, comprising means for developing a plurality of unidirectional derived current-responsive voltages,

If, however, as is assumed to be the case, the

amplifier-tube 635 is of the saturating variety, it is not necessary that its plate-voltage shall be larger than the voltage of the station-battery and and in fact, the station-battery may be utilized as the plate-voltage source of the amplifier tube, as shown in Fig. 3. In this case, the negative terminal 64 of the tube is connected to the intermediate point 28 in the grid-control circuit of the master-oscillator it, so as to bring this point substantially to the potential of the positive bus whenever the amplifier tube 63 is changed from its non-operative or non-conducting condition to its operative condition, in

response to a sufllciently large positive voltage appearing across the relaying-bus Bil-6i, which makes the amplifier-grid 65 sufficiently positive with respect to its anode B4.

In Fig. 3, the reverse-current conductivity of the various rectiflers l8 has the same effect as a certain grid-leakage resistance, which may be utilized as a grid-leak, or I may utilize an equivalent or suitable resistance R8, as shown in Fig. 3, in the same manner to which the resistance RI of Fig. 1 represents the equivalent of the reverse-current resistance of the rectifiers ill for keeping the oscillator-grid l4 connected to the negative battery-terminal whenever there is, no voltage impressed on the controlcircuit 2B-2l of Fig. 1.

The remaining connections, as shown in Figs. 3 and 4, are substantially the same as those shown in Figs. 1 and 2, except that I have omitted the voltage-responsive compensators CA and CB and CC, and I have substituted overresponsive to difierent phases of line-currents of the protected circuit; means for developing a plurality of unidirectional derived voltage-responsive voltages, responsive to diilerent phases of line-voltages of the protected circuit, circuitderived current-respensive and voltage-responsive voltages against each other in pairs, to obtain, in each case, a resultant derived voltage for that phase, and means for connecting the resultant derived voltages as a plurality of parallel-connected sources of voltage for a relaying circuit, the parallel connections including rectifiers whereby the largest of said resultant derived voltages is substantially excluded from feed-back into the circuits of the smaller of said resultant derived voltages, and fault-responsive apparatus energized from said relaying circuit.

2. Fault-responsive relaying-apparatus for a polyphase circuit which is to be protected, comprising means for developing a plurality of de rived current-responsive voltages, responsive to diilerent phases of line-currents of the protected circuit, means for developing a plurality of unidirectional derived voltage-responsive voltages, responsive to different phasesoi line-voltages of the protected circuit, circuit-means for opposing derived current-responsive and voltage-responsive voltages against each other in pairs, to obtain, in each case, a resultant derived voltage for that phase, and means for connecting the resultant derived voltages as a plurality of parallel-connected sources of voltage for a relaying circuit, the parallel connections including rectiriers whereby rectified resultant voltages are supplied to said relaying circuit, and whereby the largest of said rectified resultant voltages is substantially excluded from feed-back into the circuits of the smaller of said rectified resultant voltages, and fault-responsive apparatus energized from said relaying circuit.

3. Terminal equipment for one terminal of a direction-comparing type of carrier-current relaying-system for protecting a line-section of an alternating-current transmission line against faults, said terminal equipment comprising a carrier-current transmitter, a carrier-current receiver, relay-circuit means requiring the receipt of carrier current, by said receiver, to block a faulty relaying operation, line-energized faultdetector carrier-starter means for starting and continuously maintaining the operation of said transmitter throughout the continuance of a predetermined line-fault condition, and line- I control the operation against each other in pairs, to obtain,

magnitude, to a predetermined function of electrical conditions of the line.

4.'The invention as-defined in claim 3, characterized by saidvoltage-responsive part of the tube being a grid-circuit, and said carrierstarter means comprising a unidirectional-potential source for normally applying a negative biasing voltage to said grid-circuit, said linederived control-voltage-means being connected between a negative point of said source and said grid-circuit, and a circuit-connection including a rectifier for conducting current from said gridcircuit toward a positive point of said source.

5. The invention as defined in claim 3, characterized by said carrier-starter means comprising means for developing a unidirectional derived voltage, responsive to a line-current function, means for developing a unidirectional derived voltage, responsive to a line-voltage function, and means for applying the difference between these two derived voltages to said tube to thereof.

6. The invention as defined in claim 3, characterized by said carrier-starter means comprising means for developing a plurality of derived alternating voltages, responsive to different electrical quantities of the protected circuit, means for separately rectifying said derived alternating voltages, and means for connecting the resultant rectified voltages as a plurality of parallelconnected sources of voltage for said tube to control the operation thereof, the parallel connections including rectifiers whereby the largest of said rectified voltages is substantially excluded from feedback into the circuits of the smaller of said rectified voltages.

7. Terminal equipment for a polyphase line, as defined in claim 3, characterized by said carrierstarter means comprising means for developing a plurality of unidirectional derived currentresponsive voltages, responsive to different phases of line currents of the protected circuit, means for developing a plurality of unidirectional derived voltage-responsive voltages, responsive to different phases of line-voltages of the protected circuit, circuit-means for opposing derived current-responsive and voltage-responsive voltages in each case, a resultant derived voltage for that phase, and means for connecting the resultant derived voltages as a plurality of parallel-connected sources of voltage for said tube to control the operation thereof, the parallel connections including rectifiers whereby the largest of said resultant derived voltages is substantially excluded from feed-back into the circuits of the smaller of said resultant derived voltages.

8. Terminal equipment for a polyphase line, as defined in claim 3, characterized by said carrier-starter means comprising means for developing a plurality of derived current-responsive voltages, responsive to different phases of linecurrents of the protected circuit, means for developing a plurality of unidirectional derived voltage-responsive voltages, responsive to different phases of line-voltages of the protected circuit, circuit-means for opposing derived current-mesponsive and voltage-responsive voltages against each other in pairs, to obtain, in each case, a resultant derived voltage for that phase, and means for connecting the resultant derived voltages as a plurality of parallel-connected sources of voltage for said tube to control the operation thereof, the parallel connections including rectifiers whereby rectified resultant voltages are supplied to said tube,'and whereby the largest of said rectified resultant voltages is substantially excluded from feed-back into the circuits of the smaller of said rectified resultant voltages.

9. Terminal equipment for a protective carriercurrent relaying-system for an alternating-current line, comprising, in combination, a transmitter comprising a voltage responsive tube which causes the transmitter ,to transmit an adequate carrier-current when an. adequate controlvoltage is applied to the tube and to cease transmitting at other times, and a carrier-starter means including means for constantly applying, to said tube, a line-derivedunidirectional,

. smoothed-wave control-voltage which is responsive, in magnitude, to a predetermined function of electrical conditions of the line.

10. The invention as definedin claim 9, in combination with means for limiting the magnitude of the control voltage which is applied to said tube.

11. The invention as defined in claim 9, characterized by said carrier-starter means comprising means for developing a unidirectional derived voltage, responsive to a line-current function, means for developing a unidirectional derived voltage, responsive to a line-voltage function, and means for applying the diflerence between these two derived voltages to said tube to control the operation thereof.

12. The invention as defined in claim 9, characterized by said carrier-starter means comprising means for developing a plurality of'derived alternating voltages, responsive to difierent electrical quantities of the protected circuit, means for separately rectifying said derived alternating voltages, and means for connecting the resultant rectified voltages as a plurality of parallel-connected sources of voltage for said tube to control the operation thereof, the parallel connections including rectifiers whereby the largest of said rectified voltages is substantially excluded from feedback into the circuits of the smaller of said rectified voltages.

13. Terminal equipment for a. polyphase line, as defined in claim 9, characterized by said carrier-starter means comprising'means for developing a plurality of unidirectional derived current-responsive voltages, responsive to different phases of line currents of the protected circuit,

- means for developing a plurality of unidirectional derived voltage-responsive voltages, responsive to different phases of line-voltages of the protected circuit, circuit-means for opposing derived current-responsive and voltage-responsive voltages against each other in pairs, to obtain, in each case, a resultant derived voltage for that phase, and means for connecting the resultant derived voltages as a plurality of parallel-connected sources of voltage for said tube to control the operation thereof, the parallel connections including rectifiers whereby the largest of said resultant derived voltages is substantially excluded from feed-back into the circuits of the smaller of said resultant derived voltages.

l4. Terminal equipment for a polyphase line, as defined in claim.9, characterized by said carrier-starter means comprising means for developing a pl rality of derived current-responsive voltages, responsive to different phases of linecurrents of the protected circuit, means for developing a plurality of unidirectional derived voltage-responsive voltages, responsive to different phases of line-voltages of the protected circuit, clrcuit-means for opposing derived current-responsive and voltage-responsive voltages against each other in pairs, to obtain, in'each case, a

resultant derived voltage for that phase, and

means for connecting the resultant derived volt-' EDWIN L. HARDER.

14 announces crrEn The following references are of record in the file of this patent:

UNITED s'm'ms mm Number Name Date 1,426,826 Egerton Aug. 22, 1922 2,005,148 Ves Conte et a1. June 18, 1935 2,027,226 Goldsborough Jan. 7, 1936 2,137,865 Traver Nov. 22, 1938 2,144,499 Lenehan Jan. 17, 1939- 2242350 Harder May 20, 1941, 2,275,971 I Lenehan Mar. 10, 1942 

